Suppose I have created a button inside a custom InfoTemplate (aka 'popup') widget in my Web AppBuilder app:
<SPAN class="" style="color: var(--black-750); border: 0px; font-weight: inherit; font-size: 13px;"> </SPAN><SPAN class="" style="color: var(--blue-800); border: 0px; font-weight: inherit; font-size: 13px;">var</SPAN><SPAN class="" style="color: var(--black-750); border: 0px; font-weight: inherit; font-size: 13px;"> editButton </SPAN><SPAN class="" style="color: var(--black-750); border: 0px; font-weight: inherit; font-size: 13px;">=</SPAN><SPAN class="" style="color: var(--black-750); border: 0px; font-weight: inherit; font-size: 13px;"> </SPAN><SPAN class="" style="color: var(--blue-800); border: 0px; font-weight: inherit; font-size: 13px;">new</SPAN><SPAN class="" style="color: var(--black-750); border: 0px; font-weight: inherit; font-size: 13px;"> </SPAN><SPAN class="" style="color: #2b91af; border: 0px; font-weight: inherit; font-size: 13px;">Button</SPAN><SPAN class="" style="color: var(--black-750); border: 0px; font-weight: inherit; font-size: 13px;">({</SPAN><SPAN class="" style="color: var(--black-750); border: 0px; font-weight: inherit; font-size: 13px;">